1. Field of the Invention
The present invention relates to a device and a method for correcting converted data that is provided by an analog-to-digital (A/D) conversion circuit exhibiting non-linear conversion characteristics and, more specifically, to correcting converted data so that the conversion characteristic will be linear.
2. Description of the Related Art
Linear conversion is a desirable objective for data conversion circuits particularly since non-linearities tend to produce distortion and other undesirable effects. Japanese Patent JP-A-2005-45538 discloses a prior art technology for performing correction in connection with a pulse phase-difference encoding circuit so that the conversion characteristic of an A/D conversion circuit that exhibits a non-linear conversion characteristic will become linear.
In JP-A-2005-45538, correction begins with analog-to-digital (A/D) converting predetermined reference voltages v0, v1, and v2 in order to produce digital data conversion values or vectors d0, d1, and d2. On the other hand, arbitrary reference digital values y1 and y2 meeting a condition of y1/y2=(v1−v0)/(v2−v0)=½ are predetermined.
After x1 and x2 are obtained by performing arithmetic operations x1=d1−d0 and x2=d2−d0, a quadratic functional equation whose graph passes points, which are represented by x and y coordinates as D(x1,y1) and E(x2,y2), as well as an origin is designated as a linear correctional equation. The linear correctional equation, obtained as described above and used for generating correctional values, is used to generate a shift value x, which is calculated by subtracting d0 from data ds, which exhibits non-linearity. The value x is sent from the A/D conversion circuit, so as to produce a linearity correctional value.
An actual conversion characteristic exhibited by the above A/D conversion circuit is expressed with a curve representing the 1.4-th to 1.5-th powers of values that should be provided by the A/D conversion circuit. Consequently, when the quadratic functional equation is used for correction as it is in JP-A-2005-45538, approximation is performed merely roughly. An error in corrected converted data gets larger depending on how to designate three reference voltages relative to an input voltage domain.